As mobile devices such as smart phones and tablet PCs have been developed in recent years, thinner and slimmer display substrates have been required. Glass or tempered glass as a material having excellent mechanical properties has been generally used for a display window or a front plate of these mobile devices. However, the glass causes a weight of the mobile devices to be heavy due to its own weight, and has a problem of damage due to an external impact.
Therefore, plastic resins are being studied as a substitute for glass. A plastic resin composition is appropriate for the trend of pursuing a lighter mobile device because it is lightweight and is less likely to be broken. In particular, a composition in which a supporting substrate is coated with a hard coating layer has been proposed to achieve a composition having high-hardness and wear resistance.
As a method of improving surface hardness of a hard coating layer, a method in which the thickness of a hard coating layer increases can be considered. In order to ensure enough surface hardness to substitute for glass, it is necessary to realize a constant thickness of a hard coating layer.
As the thickness of a hard coating layer increases, surface hardness may increase. However, wrinkling or curling increases due to cure shrinkage of a hard coating layer and simultaneously a hard coating layer is likely to be cracked or peeled off. Therefore, it is not easy to practically apply the method.
Recently, several methods for realizing high-hardness of a hard coating film and simultaneously solving a problem of cracking of a hard coating layer or a curl caused by cure shrinkage have been proposed.
In Korean Patent Publication No. 2014-0027022, a hard coating composition that includes an acrylate monomer and a photocurable elastomer having elongation in a predetermined range and thus exhibits improved impact resistance is disclosed. However, the hard coating composition disclosed above does not exhibit enough bending resistance and impact resistance to substitute for a glass panel of a display.
In Korean Patent Publication No. 2011-0078783, a hard coating composition that includes 5 to 80 wt % of an alkylene-glycol-based acrylic monomer and thus exhibits improved surface hardness and impact resistance is disclosed. However, the hard coating composition disclosed above also does not exhibit enough impact resistance to substitute for a glass panel of a display.